I like the idea of working in groups especially when it is to research, evaluate, discuss, and conclude on a hot button topic. I also use the random assignment of groups. In my experience, it works more effectively for the students even if they know each other very well.
I love using learning groups because it gives students a chance to explore concepts and ideas without having a teacher looming over their shoulder.
There are formal and informal groups. Putting students in formal groups can help them learn from each other.
Working in groups that are assigned by the instructor can be beneficial for all the group members. They will have a chance to get to know their fellow classmates, share knowledge, and build rapport.
